1. Field of the Invention
The present invention relates to a trans-impedance amplifier (TIA), and in particular, to a trans-impedance amplifier for reducing propagation delay.
2. Description of Related Art
In optical communication systems, gain and sensitivity of optical receivers are important features, and both must be improved simultaneously in order to optimize transmission efficiency. Single-stage TIA used in conventional optical receivers have a simple structure, but suffers from the problem that high sensitivity cannot be achieved due to insufficient transimpedance gain, because there is a close relation between the overall gain and bandwidth characteristics and the impedance of an output of the amplifier.
Therefore, generally, the architecture of multi-stage trans-conductance amplifier (TCA) is used to design optical receivers in order to achieve high transimpedance gain. Such an architecture of multi-stage TCA usually comprises a plurality of single amplifiers in series, but because the input current of optical receivers depends on infrared light received by photodiodes, there may be a four times difference between the maximum and the minimum of the input current. This difference between the maximum and the minimum of the input current causes increased propagation delay from high to low in the potential of an output of the TIA.